This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The HIV-1 Nucleocapsid protein 7 (NCp7) is a small protein that binds to the stem-loop structures of both DNA and RNA. The recognition and folding of NCp7 and DNA/RNA stem loops play an important role in virus replication.The high field ESR was applied in addition to the X-band ESR to investigate the dynamics of Transactivation Response Element (TAR) DNA stem loop and its interaction with NCp7. The nixroxide spin labels were attached to the stem, loop, and bulge regions of TAR DNA, as well as to the 5'and 3'terminals of the DNA. Future studies to compare the multifrequency spectra of complementary TAR DNA and TAR RNA probed by spin labels in the stem, loop, and bulge regions were planned to tell the difference between the dynamics of complementary TAR DNA and TAR RNA.